Adamantane has a rigid structure and is highly symmetrical, and a derivative thereof exhibits a specific function. For these reasons, adamantane is known to be useful for highly functional resin materials, pharmaceutical intermediates, and optical materials (see Patent Documents 1 and 2), especially for photoresists (see Patent Document 3).
A resin composition for a photoresist, which is used in a semiconductor production process, needs to have characteristics, such as a property of becoming alkali-soluble when irradiated with light, etching resistance, substrate adhesiveness, transparency to a light source to be used, and the like, in a good balance. When the light source to be used is a KrF excimer laser or any other short-wavelength light source developed after the KrF excimer laser, a chemically amplified resist is generally used. The composition of such a chemically amplified resist is generally used in the form of a solution containing a resin composition as a main component, a photoacid generator and several types of additives. It is important that, among these components, the resin composition as the main component has the above-mentioned characteristics in a good balance, and the balance of the characteristics determines the performance of the resist.
When the light source to be used is a KrF excimer laser or any other short-wavelength light source developed after the KrF excimer laser, a chemically amplified resist is used. The resin composition of the chemically amplified resist, which is the main component, is generally a polymer containing acrylate or the like as a repeat unit. However, the acrylate or the like is not used as a single repeat unit. A reason for this is that a single repeat unit cannot fulfill the requirements for all the characteristics including the etching resistance. In actuality, a plurality of repeat units each having a functional group for improving each of the characteristics are used. Namely, the resin composition used is formed of a copolymer of two or more types of polymers. For a resist to be used in KrF excimer laser lithography, a hydroxystyrene-based resin is proposed; and for a resist to be used in ArF excimer laser lithography, an acrylic-based resin having 2-alkyl-2-adamantyl methacrylate as a skeleton is proposed (see Patent Documents 3 and 4).
However, recently, lithography processes have been developed so as to be usable for more and more reduced sizes, and are now required to allow each type of light source to be usable for a line width which is at most about ⅓ of the corresponding wavelength. Especially, ArF excimer laser lithography is required to be usable for a still thinner line width by means of application of immersion technology or introduction of double patterning technology. As the line width has become thinner, demands for the sensitivity, resolution, line edge roughness and the like have become more strict.
For solving these problems, it has been studied to copolymerize an existing resin with any of various acrylate compounds or to significantly change the structure itself of the existing resin. For example, a resist composition has been proposed which contains an adamantane derivative having features that the surface is not much roughened by etching, the line edge roughness is small, and the like (see Patent Document 5). However, it is currently difficult to fulfill the requirements, imposed by the reduction in the line width, for the resolution, line edge roughness and the like.